Add a knobs file to give more context about knob IDs

llvm/projects/hpvm-tensor-rt/PPoPP_results/knobs.txt

+perf_fp16,120,Baseline
+perf_fp16,151,Col perf 50% offset=0
+perf_fp16,152,Col perf 50% offset=1
+perf_fp16,153,Row perf 50% offset=0
+perf_fp16,154,Row perf 50% offset=1
+perf_fp16,155,Col perf 33% offset=0
+perf_fp16,156,Col perf 33% offset=1
+perf_fp16,157,Col perf 33% offset=2
+perf_fp16,158,Row perf 33% offset=0
+perf_fp16,159,Row perf 33% offset=1
+perf_fp16,160,Row perf 33% offset=2
+perf_fp16,161,Col perf 25% offset=0
+perf_fp16,162,Col perf 25% offset=1
+perf_fp16,163,Col perf 25% offset=2
+perf_fp16,164,Col perf 25% offset=3
+perf_fp16,165,Row perf 25% offset=0
+perf_fp16,166,Row perf 25% offset=1
+perf_fp16,167,Row perf 25% offset=2
+perf_fp16,168,Row perf 25% offset=3
+samp_fp16,261,Samp 50% offset=0
+samp_fp16,262,Samp 50% offset=1
+samp_fp16,263,Samp 33% offset=0
+samp_fp16,264,Samp 33% offset=1
+samp_fp16,265,Samp 33% offset=2
+samp_fp16,266,Samp 25% offset=0
+samp_fp16,267,Samp 25% offset=1
+samp_fp16,268,Samp 25% offset=2
+samp_fp16,269,Samp 25% offset=3